1. Field of Invention.
This invention relates to a filtering apparatus and method. More specifically, it is directed to a filtration apparatus, which uses both gravitational drainage and vacuum drainage, that is constructed for selective retrofitting into a container. The filtration apparatus extracts liquid from a sludge or slurry inside the container and separates the resulting liquids and solids for separate disposal or recovery.
Sludge includes any solid-liquid sludge and slurry such as sewage and industrial waste. The sludge may contain any ratio of liquids to solids. In fact, the sludge often has substantially more solid material than liquid material. Separation of the sludge into its liquid and solid components, also known as "dewatering," is desirable for recovery or disposal of one or both of the components.
One typical manner of dewatering sludge involves placing the sludge into a container that has filters therein. The liquid in the sludge passes through the filters and from the container. However, the filters do not permit the solids to pass therethrough. Therefore, the solids remain in the container and are removed after the dewatering operation is complete.
Generally, the fluid is drawn through the filter in one of two ways, vacuum drainage or gravitational drainage. Vacuum drainage requires the use of a pump in flow communication with the filtrate cavity of the filter. In order for the pump to develop a vacuum, the filtrate cavity must remain below the liquid surface level at all times.
Vacuum drainage often results in filter blockage. In this type of system, activation of the pump draws the sludge liquid as well as the sludge solids toward the filters. However, during the initial stages of dewatering when the liquid concentration is highest, the smaller sludge solid particles more readily flow toward the filter and tend to block the filter element. Blockage of the filter element hinders dewatering speed and efficiency.
Gravitational drainage does not require a vacuum and, therefore, does not require maintenance of the filtrate cavity below the sludge liquid surface. Consequently, the filters in such a system can extend the entire height of the container and, thereby, provide greater drainage surface area. Also, because gravitational drainage is slower than vacuum drainage, the sludge solid particles settle on the filter surface in a more uniform manner and provide an additional filtering layer. Thus, the filters do not experience blockage. However, as mentioned, gravitational drainage is relatively slow.
A filtration device which effectively and efficiently utilizes both vacuum and gravitational drainage gives a user more versatility in dewatering the sludge. In addition, the added assistance of vacuum drainage can speed up the dewatering process, extract more moisture from the sludge, and, in some cases, dewater a sludge that would not otherwise be considered feasible to dewater.
Moreover, a number of containers do not contain the filters needed for filtering the sludge because they are designed for more general purposes. Consequently, sludge dewatering generally requires special containers fitted with the needed filters. This need for specially designed dewatering containers causes waste of container resources.
2. Related Art
Filtering systems have long been known to the prior art. Illustrative of such systems are U.S. Pat. No. 301,460, U.S. Pat. No. 988,391, U.S. Pat. No. 3,446,357, and U.S. Pat. No. 4,253,955.
This Applicant's U.S. Pat. No. 5,595,654 ('654 Patent) discloses a Sludge Filtration System and Method which utilizes both gravitational drainage and vacuum drainage. However, the invention disclosed in the '654 Patent comprises a special container already pre-fitted with filters. Thus, the filters, container, and system of the '654 Patent may not be readily retrofitted for use in other general purpose containers.
Though the above mentioned filtering systems may be helpful for their stated purposes, they do not address the problem of retrofitting a general purpose container with filters to dewater sludge thereby providing faster and more efficient sludge dewatering and filtration by use of both gravitational and vacuum drainage.